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Abstract:

A prosthesis is provided comprising a substrate having a distal end and a
proximal end; and a plurality of electrodes located at or adjacent the
distal end of the substrate. The distal end of the substrate is
configured for insertion, via an incision, between first and second
tissue layers, such as the sclera and choroid in the eye. The prosthesis
tapers in thickness towards the distal end and has a substantially curved
provide profile at least on one surface so that the prosthesis can be
inserted into position without needing a guide and without causing damage
to the tissue or the prosthesis. The prosthesis can include an electrode
interface unit located at or adjacent the proximal end of the substrate
which locates between the tissue layers. An anchor portion can be
provided that extends from the substrate into the incision.

Claims:

1. A visual prosthesis for implantation between a first tissue layer and
a second tissue layer, comprising: a substrate having a distal end, a
proximal end; and top and bottom surfaces extending between the distal
end and proximal end; and a plurality of electrodes located at or
adjacent the distal end of the substrate; wherein the distal end of the
substrate is configured for insertion, via an incision, to a stimulation
position between first and second tissue layers of an eye; and wherein
the thickness of the substrate between the top and bottom surfaces tapers
towards the distal end of the substrate.

2. The prosthesis of claim 1, wherein the first and second tissue layers
are a sclera and a choroid of the eye and the distal end of the substrate
is configured for insertion, via an incision in the sclera, to a position
between the sclera and the choroid.

3. The prosthesis of claim 1, wherein, prior to insertion, at least one
of a top and bottom surface of the substrate is substantially curved
between the proximal and distal ends.

4. The prosthesis of claim 1, wherein the substrate has two opposite side
edges extending between the distal and proximal ends and prior to
insertion at least one of the top and bottom surface is substantially
curved between the side edges.

5. The prosthesis of claim 4, wherein at least one of a top and bottom
surface is substantially part-spherical between the side edges.

6. The prosthesis of claim 1, wherein: the substrate has two opposing
side edges extending between the distal and proximal ends; the first and
second tissue layers are a sclera and a choroid of the eye and the distal
end of the substrate is configured for insertion, via an incision in the
sclera, to a position between the sclera and the choroid; the top of the
substrate is substantially curved between the distal and proximal ends;
the top of the substrate is substantially part-spherical between the side
edges; and the width of the substrate between the side edges is
substantially uniform as the thickness of the substrate tapers toward the
distal end.

7. The prosthesis of claim 1, wherein the thickness of the substrate
tapers from a region at or adjacent the proximal end of the substrate.

8. The prosthesis of claim 1, wherein the thickest region of the
substrate is located at an intermediate position between the distal end
and the proximal end of the substrate.

9. The prosthesis of claim 8, wherein the thickest region of the
substrate is located closer to the proximal end of the substrate than the
distal end of the substrate.

10. The prosthesis of claim 1, wherein, prior to insertion, the bottom
surface of the substrate is a substantially flat surface.

11. The prosthesis of claim 1, wherein the distal end of the substrate is
stiff enough to be pushed into the incision without buckling, yet
flexible enough to at least substantially conform to the anatomy of the
first and second tissue layers so that the substrate can be inserted
without using a guide.

12. (canceled)

13. The prosthesis of claim 1, comprising one or more ribs or spines
located in or on the substrate and extending some or all of the distance
between the distal and proximal ends of the substrate.

14. The prosthesis of claim 1, comprising an electrode interface unit
located in or on the substrate.

15. The prosthesis of claim 14, wherein the electrode interface unit is
at or adjacent the proximal end of the substrate.

16. The prosthesis of claim 14, wherein the electrode interface unit s
configured to locate between the first and second tissue layers after
insertion of the distal end of the substrate to the stimulation position.

17. The prosthesis of any claim 1 comprising an anchor portion connected
to the substrate at or adjacent the proximal end of the substrate,
wherein the anchor portion is configured to locate in the incision after
insertion of the distal end of the substrate to the stimulation position.

18. The prosthesis of claim 1 comprising a cable, the cable extending
outwardly from the substrate and providing a means for electrically
communicating with at least one of the electrodes and an electrode
interface unit, the cable being configured to extend through the incision
when the distal end of the substrate is in the stimulation position.

19. The prosthesis of claim 17 comprising a cable, the cable extending
outwardly from the substrate and providing a means for electrically
communicating with at least one of the electrodes and an electrode
interface unit, the cable being configured to extend through the incision
when the distal end of the substrate is in the stimulation position,
wherein the cable provides at least part of the anchor portion.

20. The prosthesis of claim 17, wherein the anchor portion comprises a
substantially planar element comprising a mesh or one or more cut-out
regions.

21. The prosthesis of claim 17, wherein the anchor portion is connected
to the substrate at a position spaced from a proximal end edge of the
substrate.

22. The prosthesis of claim 21, wherein a region of the substrate
extending from the anchor portion to the proximal end edge of the
substrate provides a stabilizing tail for the substrate, the stabilizing
tail being configured to locate to the opposite side of the incision from
the distal end of the substrate when the distal end of the substrate is
located in the stimulation position

23. The prosthesis of claim 1 comprising a bumper projecting from a
distal end edge of the substrate.

24. The prosthesis of claim 23, comprising a bumper projecting from at
least one of a proximal end edge and side edges of the substrate.

25. The prosthesis of claim 18, wherein the cable is a stretchable cable.

26. The prosthesis of claim 25, wherein the stretchable cable is a
helical, twisted or curved cable.

27. The prosthesis of claim 18, wherein the cable is electrically
connected to at least one of the electrodes and the electrode interface
unit via stretchable wiring extending through the substrate.

28. The prosthesis of claim 27, wherein the stretchable wiring is
helical, twisted or curved wiring.

29. The prosthesis of claim 1, comprising a patch and a cable, wherein
the cable extends outwardly from the substrate and providing a means for
electrically communicating with the electrodes, the cable being
configured to extend through the incision when the distal end of the
substrate is in the stimulation position; and the patch is configured for
locating across at least a portion of the incision at the surface of the
first tissue layer to support the cable as it exits the incision.

30. The prosthesis of claim 29, wherein the patch is configured to fix a
bend in the cable upon exiting the incision,

31. The prosthesis of claim 29, wherein the patch is fixed to the cable
during insertion of the substrate.

32. (canceled)

33. A visual prosthesis for implantation between a sclera and a choroid,
comprising: a substrate having a distal end and a proximal end; a
plurality of electrodes located at or adjacent the distal end of the
substrate; and an electrode interface unit located at or adjacent the
proximal end of the substrate and electrically connected to the
electrodes via a plurality of electrical conductors; wherein the distal
end of the substrate is configured for insertion, via an incision in the
sclera, to a stimulation position between the sclera and choroid,
whereupon the electrode interface unit also locates between the sclera
and choroid.

34. A method of implanting a visual prosthesis in an eye, the visual
prosthesis comprising: a substrate having a distal end and a proximal
end; a plurality of electrodes located at or adjacent the distal end of
the substrate; and an electrode interface unit located at or adjacent the
proximal end of the substrate and electrically connected to the
electrodes via a plurality of electrical conductors, wherein the method
comprises: making an incision in a sclera; inserting the distal end of
the substrate through the incision in the sclera; locating the distal end
of the substrate at or adjacent a stimulation position between the sclera
and choroid; and locating the electrode interface unit between the sclera
and choroid.

35. A visual prosthesis for implantation between a sclera and choroid,
comprising: a substrate having a distal end and a proximal end; a
plurality of electrodes located at or adjacent the distal end of the
substrate; and an anchor portion connected to the substrate at or
adjacent the proximal end of the substrate; wherein the distal end of the
substrate is configured for insertion, via an incision in the sclera, to
a stimulation position between the sclera and choroid, whereupon the
anchor portion locates in the incision in the sclera.

36. A method of implanting a visual prosthesis in an eye, the visual
prosthesis comprising: a substrate having a distal end and a proximal
end; a plurality of electrodes located at or adjacent the distal end of
the substrate; and an anchor portion connected to the substrate at or
adjacent the proximal end of the substrate, wherein the method comprises:
making an incision in a sclera; inserting the distal end of the substrate
through the incision in the sclera; locating the distal end of the
substrate at a stimulation position between the sclera and choroid; and
locating the anchor portion in the incision in the sclera.

37. (canceled)

38. A visual prosthesis for implantation between a sclera and choroid
comprising: a substrate having a distal end and a proximal end; a
plurality of electrodes located at or adjacent the distal end of the
substrate; and one or more ribs or spines provided in or on the substrate
and extending some or all of the distance between the proximal and distal
ends of the substrate; wherein the distal end of the substrate is
configured for insertion, via an incision in the sclera, to a stimulation
position between the sclera and choroid.

39. A tissue stimulation or sensing device for implantation between a
first tissue layer and a second tissue layer, comprising: a substrate
having a distal end and a proximal end, a plurality of electrodes located
at or adjacent the distal end of the substrate for stimulating tissue or
sensing electrical activity in the tissue, and an electrode interface
unit located at or adjacent the proximal end of the substrate and
electrically connected to the electrodes via a plurality of electrical
conductors; wherein the distal end of the substrate is configured for
insertion, via an incision in a first tissue layer, to a stimulation or
sensing position between the first tissue layer and a second tissue layer
directly adjacent to the first tissue layer, whereupon the electrode
interface unit also locates between the first and second tissue layers.

40. A method of implanting a tissue stimulation or sensing device in
tissue, the device comprising: a substrate having a distal end and a
proximal end; a plurality of electrodes located at or adjacent the distal
end of the substrate for stimulating or sensing electrical activity in
tissue, and an electrode interface unit located at or adjacent the
proximal end of the substrate and connected to the electrodes via a
plurality of electrical conductors, wherein the method comprises: making
an incision in a first tissue layer; inserting the distal end of the
substrate through the incision in the first tissue layer; locating the
distal end at a stimulation or sensing position between the first tissue
layer and a second tissue layer directly adjacent to the first tissue
layer; and locating the electrode interface unit between the first and
second tissue layers.

41. A tissue stimulation or sensing device comprising: a substrate having
a distal end and a proximal end; a plurality of electrodes located in or
on the substrate for stimulating tissue or sensing electrical activity in
the tissue; and an anchor portion connected to the substrate at or
adjacent the proximal end of the substrate; wherein the distal end of the
substrate is configured for insertion, via an incision in a first tissue
layer, to a stimulation position between the first tissue layer and a
second tissue layer, whereupon the anchor portion locates in the incision
in the first tissue layer.

42. A method of implanting a tissue stimulation or sensing device in
tissue, the device comprising: a substrate having a distal end and a
proximal end; a plurality of electrodes located in or on the substrate
for stimulating tissue or sensing electrical activity in the tissue; and
an anchor portion connected to the substrate at or adjacent the proximal
end of the substrate, wherein the method comprises: making an incision in
a first tissue layer; inserting the distal end of the substrate through
the incision in the first tissue layer; locating the distal end at a
stimulation or sensing position between the first tissue layer and a
second tissue layer; and locating the anchor portion in the incision in
the first tissue layer.

43. A device for implantation between a first tissue layer and a second
tissue layer, comprising: a substrate having a distal end, proximal end;
top and bottom surfaces extending between the distal end and proximal
end, and a plurality of electrodes located in or on the substrate;
wherein the distal end of the substrate is configured for insertion, via
an incision, to a stimulation position between first and second tissue
layers; and wherein the thickness of the substrate between the top and
bottom surfaces tapers towards the distal end of the substrate.

44. A for implantation between a first tissue layer and a second tissue
layer, comprising: a substrate having a distal end and a proximal end; a
plurality of electrodes located in or on the substrate for stimulating
tissue or sensing electrical activity in the tissue; and one or more ribs
or spines provided in or on the substrate and extending some or all of
the distance between the proximal and distal ends of the substrate,
wherein at least a portion of the substrate is configured for insertion,
via an incision, to a stimulation position between first and second
tissue layers.

Description:

FIELD OF THE INVENTION

[0001] The present patent application relates to apparatus for stimulating
tissue and/or monitoring activity in tissue, particularly, although not
necessarily exclusively, an apparatus for stimulating retinal cells of a
patient to restore or improve vision.

BACKGROUND

[0002] Visual prostheses have been developed to restore vision within
blind or partially blind patients. A visual prosthesis commonly includes
an implantable component including an electrode array, situated on or in
a substrate, for placement in the eye on or near retinal cells.
Electrical signals are transmitted via the electrodes to the retinal
cells, triggering a perception of light within the patient's brain. The
prosthesis can therefore restore vision to patients whose retinal
photoreceptors have become dysfunctional.

[0003] Commonly, a visual prosthesis is used in conjunction with a video
camera. A stream of images detected by the camera is converted into
digital signals by an image processor and transmitted in `real time` to
an electrode interface unit. The electrode interface unit is connected to
the electrode array via a plurality of conductors and decodes the signals
and stimulates the electrodes in accordance with the detected images.

[0004] The digital signals can be transmitted wirelessly, at least part or
all of the way between the processor and the implantable component. A
wireless receiver for receiving the wireless signals can be located on
the substrate, or separate to the substrate.

[0005] The substrate of the prosthesis can been located in a variety of
positions to stimulate the retina. One approach is to place the
electrode-carrying part of the substrate between the sclera and the
choroid, i.e. into the suprachoroidal space. For example, US 2009/0177245
A1 and US 2006/0074461 A1 each disclose an electrode array placed
suprachoroidally, the electrode array being connected via a connecting
cable, extending through an incision in the sclera, to an interface unit
located to the outside of the sclera (i.e., episclerally). The cable
takes the form of a ribbon cable, comprising a plurality of wires
connecting individual electrodes to the interface unit.

[0006] Any discussion of documents, acts, materials, devices, articles or
the like which has been included in the present specification is solely
for the purpose of providing a context for the present invention. It is
not to be taken as an admission that any or all of these matters form
part of the prior art base or were common general knowledge in the field
relevant to the present invention as it existed before the priority date
of each claim of this application.

[0007] Throughout this specification the word "comprise", or variations
such as "comprises" or "comprising", will be understood to imply the
inclusion of a stated element, integer or step, or group of elements,
integers or steps, but not the exclusion of any other element, integer or
step, or group of elements, integers or steps.

[0008] Throughout this specification the term "visual prosthesis" is used
to denote apparatus for restoring or improving a patient's vision, and
will be understood to include devices otherwise known as bionic eyes,
artificial eyes, retinal prostheses and retinal stimulators or similar.

SUMMARY

[0009] According to a first aspect, the present invention provides a
visual prosthesis comprising:

[0010] a substrate having a distal end and a proximal end;

[0011] a plurality of electrodes located at or adjacent the distal end of
the substrate; and

[0012] an electrode interface unit located at or adjacent the proximal end
of the substrate and electrically connected to the electrodes via a
plurality of electrical conductors;

[0013] wherein the distal end of the substrate is configured for
insertion, via an incision in the sclera, to a stimulation position
between the sclera and choroid, whereupon the electrode interface unit
also locates between the sclera and choroid.

[0014] According to a second aspect, the present invention provides a
method of implanting a visual prosthesis in an eye, the visual prosthesis
comprising: a substrate having a distal end and a proximal end; a
plurality of electrodes located at or adjacent the distal end of the
substrate; and an electrode interface unit located at or adjacent the
proximal end of the substrate and electrically connected to the
electrodes via a plurality of electrical conductors, wherein the method
comprises:

[0015] making an incision in the sclera;

[0016] inserting the distal end of the substrate through the incision in
the sclera;

[0017] locating the distal end of the substrate at or adjacent a
stimulation position between the sclera and choroid; and

[0018] locating the electrode interface unit between the sclera and
choroid.

[0019] Prior to locating the distal end of the substrate at or adjacent a
stimulation position between the sclera and choroid, preferably a pocket
is created between the sclera and choroid, in the suprachoroidal space.
The pocket may be created using a tool such as a rounded blade or
crescent blade that is inserted through the incision in the sclera before
separating the sclera and choroid. The pocket may serve as a predefined
space for introducing the distal end of the substrate and may ensure that
the substrate remains in the correct anatomical plane between the sclera
and choroid as the distal end is advanced to the stimulation position.
The depth of the pocket prior to insertion of the substrate may be
shorter than the length of the substrate, and the pocket may be
lengthened subsequently by the movement of the substrate as it advances
into position. The depth of the pocket created prior to insertion of the
substrate may be defined by the length of the tool. The substrate may
include a depth marker to indicate when the tip of the substrate has
reached the end of the pocket created by the tool.

[0020] An anchor portion may be connected to the substrate at or adjacent
the proximal end of the substrate. The anchor portion can be suitable for
anchoring a proximal portion or the proximal end of the substrate in a
desired position. The anchor portion can be arranged to locate within the
incision in the sclera.

[0021] The prosthesis and method of the first and second aspects can have
one, some or all of the features of the prosthesis and method
respectively, as defined herein with regard to other aspects.

[0022] According to a third aspect, the present invention provides a
visual prosthesis comprising:

[0023] a substrate having a distal end and a proximal end;

[0024] a plurality of electrodes located at or adjacent the distal end of
the substrate; and

[0025] an anchor portion connected to the substrate at or adjacent the
proximal end of the substrate;

[0026] wherein the distal end of the substrate is configured for
insertion, via an incision in the sclera, to a stimulation position
between the sclera and choroid, whereupon the anchor portion locates in
the incision in the sclera.

[0027] According to a fourth aspect, the present invention provides a
method of implanting a visual prosthesis in an eye, the visual prosthesis
comprising: a substrate having a distal end and a proximal end; a
plurality of electrodes located at or adjacent the distal end of the
substrate; and an anchor portion connected to the substrate at or
adjacent the proximal end of the substrate, wherein the method comprises:

[0028] making an incision in the sclera;

[0029] inserting the distal end of the substrate through the incision in
the sclera;

[0030] locating the distal end of the substrate at a stimulation position
between the sclera and choroid; and

[0031] locating the anchor portion in the incision in the sclera.

[0032] The prosthesis and method of the third and fourth aspects can have
one, some or all of the features of the prosthesis and method
respectively, as defined herein with regard to other aspects. For
example, an electrode interface unit may be located at or adjacent the
proximal end of the substrate and electrically connected to the
electrodes via a plurality of electrical conductors. However, the
electrode interface unit may also be located separately to the substrate,
e.g., externally to the eye.

[0033] By anchoring the proximal portion or proximal end of the substrate,
the proximal portion or end may be fixed in position whilst the
remainder, or at least the distal end, of the substrate `floats` between
the sclera and the choroid. One or more sutures can be used to connect
the anchor portion to body tissue, e.g., the sclera, at the location of
the incision. The suture can be used to both close the incision and
connect the anchor portion to the tissue.

[0034] The anchor portion may be a projection from the substrate, e.g., a
substantially planar element such as a flap of material projecting from
the substrate. The projection may be pivotable about its connection with
the substrate. The material may be a polymeric material, for example a
polyester such as Dacron®. The anchor portion may be a continuous
piece of material, or it may be a mesh, and/or comprise one or more
cut-out portions. If one or more cut out portions are provided in or near
the centre of the anchor portion, the peripheral edges of the anchor
portion may provide for anchoring of the substrate, whilst healing of the
incision by scleral tissue reconnecting through the cut out sections can
take place.

[0035] As an alternative, or additionally, the anchor portion may be
provided by a cable (i.e., a lead). The cable may serve as a means of
electrically communicating with the plurality of electrodes, whilst also
providing anchoring function.

[0036] The length of the substrate between its proximal and distal ends
may be chosen to achieve the desired insertion arrangement, depending on
the position at which the incision is made in the sclera relative to the
intended stimulation position. The length may be 18 to 28 mm, for
example. The incision in the sclera can be towards the front of the eye,
e.g., about 4 mm to 8 mm, e.g., 5 mm, behind the limbus. This position
may provide for relatively easy surgical access, wound repair and access
to a space between the sclera and choroid sufficiently recessed from the
stimulation position to fit the electrode interface unit. The anchor
portion can be connected to the substrate at about 12 mm to 28 mm from
the distal end tip of the substrate, e.g., at 20 or 26 mm from the distal
end tip. The electrodes may be located within a region of the substrate
extending about 5 mm to 20 mm from the distal end tip. The substrate may
be about 5 to 14 mm wide.

[0037] The anchor portion may be connected at a position spaced inwards
from the proximal end, leaving a lip of the substrate to extend
proximally from the anchor portion to a proximal end edge. The lip can
project to the opposite side of the connection with the anchor portion to
that of the distal end of the substrate. The lip may be 1 to 3 mm long,
for example. By having a portion of the substrate extending proximally
from the connection with the anchor portion, the substrate and anchor
portion can seat relatively more stably against scleral tissue at the
incision region. The portion may provide, in essence, a stabilizing tail
to the substrate, and may support tissue around the incision and minimise
the risk of leakage and choroidal incarceration.

[0038] In any of the aspects described herein, insertion of the substrate
may be carried out using forceps, such as soft-tipped forceps to prevent
damage. The substrate may be inserted to a point where the tip is between
about 2 mm and 4 mm from the optic disc (head of the optic nerve). To
assist in achieving the desired insertion depth, depth insertion markers
may be placed on the substrate. One or more different depth markers may
be provided to address different eye sizes and/or different incision
points in the sclera. To prevent the substrate from being inserted
back-to-front, or the wrong way round, the substrate may also or instead
include left and right side indicators, outside and inside indicators
and/or a distal tip indicator. The distal tip indicator may be an arrow
or other indicia indicative of the direction in which the substrate is to
be inserted into the incision. After the insertion of the substrate, the
incision may be closed, e.g., using sutures such as dissolving or
non-dissolving sutures.

[0039] The plurality of conductors connecting the electrodes and the
interface unit, whether the interface is located in the substrate or
elsewhere, may take the form of electrically conducting wires, such as
metal wires, e.g., platinum wires. The conductors can be electrically
insulated from one another, and/or electrically insulated from
surrounding eye tissue at least partially along their length. At or
adjacent the distal end of the substrate, electrical insulation may be
omitted in order to form the electrodes. However, other types of
electrodes such as disk electrodes with e.g., 0.2 to 0.8 mm diameter may
be used. The conductors can extend within the substrate. The conductors
can take the form in combination with the substrate of a ribbon cable.
Alternatively, the conductors may take the form of one or more coiled
wires. The coiled wires may be located within a conduit in the substrate
or in a sheath as part of a cable external to substrate. The cable
extending from the substrate, including the sheath, may be coiled. By
using coiled wire and cable, the wire and cable may be stretchable,
allowing for stretching as the substrate flexes or the cable flexes,
e.g., during insertion of the substrate in the eye or during subsequent
use of the implanted substrate, e.g., when the eye rotates. Other types
of stretchable wire or cable may be used, such as twisted, curved or zig
zag wires or cables.

[0040] The plurality of conductors can terminate at the electrode
interface unit, meaning that there is no requirement for these conductors
to exit the sclera if the electrode interface unit is located in or on
the substrate. In essence, the substrate can be configured to be sealed
entirely within the bounds of the sclera. Signals generated outside the
eye, such as signals for stimulating the electrodes, may be transmitted
to the interface unit of the substrate via a relatively small cable (this
can be a cable with a non-flat configuration (a `round cable`), such as a
cable with a substantially circular cross-section) or wirelessly. If
wireless transmission is used, the point of incision in the sclera may be
closed completely, or, if a round cable is used, to a greater degree than
if a ribbon cable (e.g. the substrate itself) were to extend out of the
incision. In this regard, the likelihood of scleral lesions or choroid
rupture is relatively reduced compared to arrangements which rely on use
of a ribbon cable extending through the location of the incision.

[0041] The incision in the sclera and adjacent region between the sclera
and choroid may provide a particularly compliant region and/or large open
space for locating the anchor portion and electrode interface unit. The
proximal portion of the substrate may have a relatively wider
configuration than a distal portion of the substrate, enabling a
relatively larger interface unit or more than one interface unit to be
located in the substrate. In this regard, the substrate may take a "T"
shape or an "L" shape. The choroid provides a natural heat sink for the
components of the interface unit, providing effective heat dissipation
and improving component performance.

[0042] In any of the aspects described herein, the incision may be
straight, curved or angular at its opening on the surface of the sclera.
For example, particularly to enable accommodation of a cable or lead
extending from the substrate, the incision may take an "L" shape, formed
from two substantially straight cuts extending perpendicularly to each
other. The substrate may be inserted through one of the cuts and, during
or after insertion, the cable may extend out of the incision via the
other of the cuts.

[0043] The distal portion of the substrate and the electrodes thereon may
be configured for stimulating retinal cells. Further, the stimulation
need not stimulate only a central region of the patient's vision, but
also peripheral regions of the patient's vision. To achieve this, the
electrodes may be spread over a relatively large area of the substrate.

[0044] During implantation of the prosthesis, the distal end of the
substrate may be pushed into position between the sclera and choroid
without using a guide.

[0045] According to a fifth aspect, the present invention provides a
visual prosthesis comprising:

[0046] a substrate having a distal end and a proximal end; and

[0047] a plurality of electrodes located at or adjacent the distal end of
the substrate

[0048] wherein the distal end of the substrate is configured for
insertion, via an incision in the sclera, to a stimulation position
between the sclera and choroid, without using a guide.

[0049] According to a sixth aspect, the present invention provides a
method of implanting a visual prosthesis in an eye, the visual prosthesis
comprising: a substrate having a distal end and a proximal end; and a
plurality of electrodes located at or adjacent the distal end of the
substrate; wherein the method comprises:

[0050] making an incision in the sclera;

[0051] inserting the distal end of the substrate through the incision in
the sclera; and

[0052] locating the distal end at a stimulation position between the
sclera and choroid without using a guide.

[0053] In any of the above aspects, by not using a guide (such as a guide
wire), during the insertion process, only the prosthesis need be inserted
between the sclera and choroid, or only the prosthesis need be inserted
through the incision in the sclera and between the sclera and choroid.
Steering of the prosthesis to the stimulation position may be through use
of the forceps to the outside of the incision only. So that a guide need
not be used, an appropriate stiffness for the substrate may be chosen.
The substrate can be stiff enough to be pushed into position without
buckling (e.g., rolling), yet flexible enough to conform to the anatomy
of the sclera and choroid. When a guide is not used, insertion of the
prosthesis may be simplified and the chances of damaging eye tissue
during insertion may be reduced.

[0054] The prosthesis and method of the fifth and sixth aspects can have
one, some or all of the features of the prosthesis and method
respectively, as defined herein with regard to other aspects.

[0055] According to a seventh aspect, the present invention provides a
visual prosthesis comprising:

[0056] a substrate having a distal end and a proximal end; and

[0057] a plurality of electrodes located at or adjacent the distal end of
the substrate;

[0058] wherein the distal end of the substrate is configured for
insertion, via an incision in the sclera, to a stimulation position
between the sclera and choroid, the distal end of the substrate being
stiff enough to be pushed into position without buckling, yet flexible
enough to at least substantially conform to the anatomy of the sclera and
choroid.

[0059] According to an eighth aspect, the present invention provides a
method of implanting a visual prosthesis in an eye, the visual prosthesis
comprising: a substrate having a distal end and a proximal end; and a
plurality of electrodes located at or adjacent the distal end of the
substrate for stimulating the retina, wherein the method comprises:

[0060] making an incision in the sclera;

[0061] inserting the distal end of the substrate through the incision in
the sclera; and

[0062] locating the distal end at a stimulation position between the
sclera and choroid,

[0063] wherein the distal end of the substrate is stiff enough to be
pushed into position without buckling, yet flexible enough to at least
substantially conform to the anatomy of the sclera and choroid.

[0064] The prosthesis and method of the seventh and eighth aspects can
have one, some or all of the features of the prosthesis and method
respectively, as defined herein with regard to other aspects.

[0065] In any of the aspects, to realise a substrate with the desired
stiffness and flexibility, an appropriate material and/or thickness
and/or surface profile of the substrate may be chosen. The material may
be a flexible polymer, such as polyimide. The substrate may taper toward
the distal end, permitting relatively greater flexing at the distal end
region.

[0066] According to a ninth aspect, the present invention provides a
visual prosthesis comprising:

[0067] a substrate having a distal end, a proximal end; and top and bottom
surfaces extending between the distal end and proximal end, and

[0068] a plurality of electrodes located at or adjacent the distal end of
the substrate;

[0069] wherein the distal end of the substrate is configured for
insertion, via an incision, to a stimulation position between the sclera
and choroid; and

[0070] wherein the thickness of the substrate between the top and bottom
surfaces tapers toward the distal end of the substrate.

[0071] In any of the aspects, to provide the tapering, one or both of the
top and bottom surfaces of the substrate may have a substantially curved
profile between the proximal and distal ends, i.e., in the longitudinal
direction of the substrate. When only one of the top and bottom surfaces
of the substrate has a substantially curved profile between the proximal
and distal ends, the other of the top and bottom surfaces may be
substantially flat. For example, the top surface, which may be for
locating adjacent the sclera, may have a curved profile in the
longitudinal direction of the substrate, whereas the bottom surface,
which may be for locating adjacent the choroid, may be substantially
flat. Although the thickness of the substrate may taper toward the distal
end, the width of the substrate may be substantially uniform at least
throughout this tapering portion. The substrate may taper from a
thickness of 0.8 mm to 0.15 mm, for example.

[0072] The thickest part of the substrate may be at or adjacent the
proximal end of the substrate. The thickest part of the substrate may be
at an intermediate position between the proximal and distal ends. When
the thickest part is at an intermediate position between the proximal and
distal ends, the thickness of the substrate may also taper towards the
proximal end. Nonetheless, the thickest part of the substrate may be
nearer to the proximal end than the distal end, which may mean that
maximum flexibility is provided at the distal end rather than the
proximal end of the substrate.

[0073] The substrate may taper in thickness towards each side of the
substrate, from a central region of the substrate, in the lateral
direction of the substrate. One or both of the top and bottom surfaces of
the substrate may have a substantially curved profile between the sides
of the substrate, i.e. in the lateral direction of the substrate. The
profile of the top and/or bottom of the substrate may be part-spherical
in the lateral direction, for example. This may ensure that the substrate
conforms to the shape of the choroid and/or sclera to improve ease of
insertion and to ensure that the substrate fits neatly between the tissue
layers.

[0074] The prosthesis of the ninth aspect can have one, some or all of the
features of the prosthesis as defined herein with regard to other
aspects.

[0075] In any of the aspects, the substrate may have a composite
construction with a relatively stiffer core region and a relatively
softer outer region. For example, the substrate may comprise one or more
longitudinally extending ribs or spines to maintain the desired stiffness
in the insertion direction to prevent buckling, whilst permitting the
substrate to bend laterally to the contours of the sclera and choroid.

[0076] According to a tenth aspect, the present invention provides a
visual prosthesis comprising:

[0077] a substrate having a distal end and a proximal end; and

[0078] a plurality of electrodes located at or adjacent the distal end of
the substrate; and

[0079] one or more ribs or spines provided in or on the substrate and
extending some or all of the distance between the proximal and distal
ends of the substrate;

[0080] wherein the distal end of the substrate is configured for
insertion, via an incision in the sclera, to a stimulation position
between the sclera and choroid.

[0081] In any of the aspects, the one or more ribs or spines may extend
parallel or at an angle to the longitudinal axis of the substrate and may
be located centrally or offset from centre, in the lateral direction of
the substrate. Where more than one rib or spine is provided, they are
preferably spaced apart in the lateral direction of the substrate. The
ribs or spines may be located on the top or bottom surface, or between
the top and bottom surface, of the substrate and may be formed of a
different material to a surrounding portion of the substrate, e.g. formed
of a relatively more dense material. The ribs or spines may be formed
integrally with the rest of the substrate, or may be inserted into the
substrate and may be of silicone or polyimide. In one embodiment, the
electrical conductors connected between the electrodes and interface unit
may be bundled together to form one or more ribs or spines, and in
another embodiment slots may be disposed in the substrate for increased
flexibility.

[0082] Further, in any of the aspects described herein, to enable the
substrate to flex laterally, when an electrode interface unit is
comprised in the substrate, the electrode interface unit may be divided
into two or more sections, spaced apart laterally, at or adjacent the
proximal end of the substrate. The proximal portion of the substrate may
therefore bend about a central region between the two sections of the
interface unit. In general, components of the visual prosthesis embedded
or located in or on the substrate may be spaced apart, with zones of
relatively high flexibility being located between these components to
enable the substrate to conform at least substantially to the contours of
the sclera and choroid. A relatively soft, conformable and biocompatible
coating (e.g. silicone or polyurethane) may be applied to the substrate
over these zones, or indeed over the entirety or other areas of the
substrate. Additionally or alternatively, the substrate may be pre-formed
to at least substantially follow the contours of the sclera and choroid,
and/or the substrate may be formed such that it is biased to take up a
configuration, upon insertion, that at least substantially follows the
contours of the sclera and choroid, e.g. take up a substantially
partspherical shape as discussed in preceding aspects.

[0083] The prosthesis and method of the tenth aspect can have one, some or
all of the features of the prosthesis and method respectively, as defined
herein with regard to other aspects.

[0084] In any of the above aspects, to prevent damage to the sclera,
choroid, or the optic disc upon insertion, the distal tip of the
substrate at its distal portion may be relatively thin in comparison to
the rest of the substrate and/or may take a rounded form. A bumper may be
located at the tip and/or lateral edges of the substrate, which bumper
may be formed from the same or a different material to the rest of the
substrate. The bumper may be a portion of relatively thin, soft and/or
smooth material projecting from the edges of the substrate. The bumper
may be silicone or polyurethane and the remainder of the substrate may be
polyimide, for example. The bumper may be flexible yet provide an
antiroll tip to the distal end edge of the substrate and may be 0.5 to 3
mm long, for example.

[0085] The visual prosthesis of any of the above aspects may be comprised
in vision restoration apparatus, the apparatus comprising, additionally:
[0086] an image receiver for receiving a stream of images; [0087] an
image processor for converting the stream of images received by the image
receiver into electrical signals; [0088] a wireless transmitter connected
to the image processor for transmitting the electrical signals
wirelessly; and/or [0089] a wireless receiver connected to the electrode
interface unit for receiving the electrical signals from the wireless
transmitter.

[0090] The image receiver may be a video camera and may be located on
eyeglass frames. The wireless receiver may be positioned with the
electrode interface unit at or adjacent the proximal end of the
substrate, and thus may be located entirely within the eye, e.g., between
the sclera and the choroid. Alternatively, the wireless receiver may be
located outside the eye and may be connected to the electrodes via a
cable that exits the eye, e.g., through an incision in the sclera. The
wireless receiver may be positioned on the surface of the eye or on the
skull at the side or rear of the patient's head.

[0091] The cable may be stabilised at the scleral incision exit to
minimise flexing, preventing damage to the surrounding tissue.
Stabilisation may be achieved using one or more anchors. One or more of
the anchors may comprise Dacron® and/or silicone material, and may be
formed at least in part as a mesh, e.g., an open Dacron® mesh. One or
more of the anchors may take the form of a patch. The anchors may extend
over the cable and may be fixed at their sides to the outer surface of
the sclera (and/or other parts of the user's head as the cable extends to
the wireless receiver). The anchor may be adhered to the cable and/or
fixed either side of the cable using sutures, e.g., Nylon 8.0 sutures.
The anchor may be coated, e.g., Parylene coated, e.g., with silicone, to
avoid unwanted adhesion between the anchor and body tissue. The cable may
be a helical lead with high flex properties. This may permit it to flex
as the eye is rotated, without causing damage to tissue at its exit point
from the sclera. The anchors may be positioned strategically to prevent
any obstruction to the extraocular muscles that cause the eye to rotate.
Preferably at least one anchor (e.g., a scleral patch) is located on the
surface of the sclera close to, or over, the incision to support the
cable as it exits the incision.

[0092] According to one aspect of the invention, there is provided a
scleral patch in combination with a visual prosthesis according to any
one of the preceding aspects.

[0093] The scleral patch may force a change in direction of extension of
the cable. For example, the patch may fix a bend in the cable, the bend
being such that the cable extends in a desirable direction as it travels
further from the incision. Preferably the patch is glued to the cable to
provide stress relief for the highly movable cable. The patch may
comprise silicone such as reinforced silicone. The patch may be connected
to the cable during insertion of the substrate in the eye.

[0094] The electrode interface unit may decode the electrical signals and
convert the signals into a plurality of individual signals for
transmitting to each electrode. The electrode interface unit may comprise
one of more switching circuits, e.g., cross point switch matrices, to
allow communication with each electrode. There can be 30 electrodes or
more, although any number of electrodes may be used. In one embodiment,
98 electrodes are provided. Preferably, when the electrode interface unit
is comprised in or on the substrate, the electrode interface unit is
hermetically sealed, e.g., to protect electronic components of the
electrode interface unit from damage by body fluids and/or to protect the
patient from exposure to chemicals contained in electronic components of
the electrode interface unit. One or more electrically conductive feed
through portions may be located on a wall of a casing of the electrode
interface unit, the feed through portions being connected to the
electrical conductors and allowing electrical communication between
electrical components located within the casing and the plurality of
electrodes, whilst ensuring that the casing is hermetically sealed.

[0095] It is envisaged that the visual prosthesis as described in any one
of the aspects above could be adapted as a device for tissue stimulation,
or the sensing of electrical activity in tissue, in others areas of the
body. In essence, instead of the tissue layers being the sclera and
choroid of the eye, the tissue layers may be any directly adjacent tissue
layers of the body at a point where tissue stimulation or the sensing of
electrical activity in tissue is to be carried out.

[0096] According to an eleventh aspect, the present invention provides a
tissue stimulation or sensing device comprising:

[0097] a substrate having a distal end and a proximal end,

[0098] a plurality of electrodes located at or adjacent the distal end of
the substrate for stimulating tissue or sensing electrical activity in
the tissue,

[0099] an electrode interface unit located at or adjacent the proximal end
of the substrate and electrically connected to the electrodes via a
plurality of electrical conductors;

[0100] wherein the distal end of the substrate is configured for
insertion, via an incision in a first tissue layer, to a stimulation or
sensing position between the first tissue layer and a second tissue layer
directly adjacent to the first tissue layer, whereupon the electrode
interface unit also locates between the first and second tissue layers.

[0101] According to a twelfth aspect, the present invention provides a
method of implanting a tissue stimulation or sensing device in tissue,
the device comprising: a substrate having a distal end and a proximal
end; a plurality of electrodes located at or adjacent the distal end of
the substrate for stimulating or sensing electrical activity in tissue,
and an electrode interface unit located at or adjacent the proximal end
of the substrate and connected to the electrodes via a plurality of
electrical conductors, wherein the method comprises:

[0102] making an incision in a first tissue layer;

[0103] inserting the distal end of the substrate through the incision in
the first tissue layer;

[0104] locating the distal end at a stimulation or sensing position
between the first tissue layer and a second tissue layer directly
adjacent to the first tissue layer; and

[0105] locating the electrode interface unit between the first and second
tissue layers.

[0106] According to a thirteenth aspect, the present invention provides a
tissue stimulation or sensing device comprising:

[0107] a substrate having a distal end and a proximal end;

[0108] a plurality of electrodes located at or adjacent the distal end of
the substrate for stimulating tissue or sensing electrical activity in
the tissue; and

[0109] an anchor portion connected to the substrate at or adjacent the
proximal end of the substrate;

[0110] wherein the distal end of the substrate is configured for
insertion, via an incision in a first tissue layer, to a stimulation
position between the first tissue layer and a second tissue layer,
whereupon the anchor portion locates in the incision in the first tissue
layer.

[0111] According to a fourteenth aspect, the present invention provides a
method of implanting a tissue stimulation or sensing device in tissue,
the device comprising: a substrate having a distal end and a proximal
end; a plurality of electrodes located at or adjacent the distal end of
the substrate for stimulating tissue or sensing electrical activity in
the tissue; and an anchor portion connected to the substrate at or
adjacent the proximal end of the substrate, wherein the method comprises:

[0112] making an incision in a first tissue layer;

[0113] inserting the distal end of the substrate through the incision in
the first tissue layer;

[0114] locating the distal end at a stimulation or sensing position
between the first tissue layer and a second tissue layer; and

[0115] locating the anchor portion in the incision in the first tissue
layer.

[0116] According to a fifteenth aspect, the present invention provides a
tissue stimulation or sensing device comprising:

[0117] a substrate having a distal end, proximal end; top and bottom
surfaces extending between the distal end and proximal end, and

[0118] a plurality of electrodes located in or on the substrate;

[0119] wherein the distal end of the substrate is configured for
insertion, via an incision in the first tissue layer, to a stimulation
position between the first and second tissue layers; and

[0120] wherein the thickness of the substrate between the top and bottom
surfaces tapers towards the distal end of the substrate.

[0121] According to a sixteenth aspect, the present invention provides a
tissue stimulation or sensing device comprising:

[0122] a substrate having a distal end and a proximal end;

[0123] a plurality of electrodes located in or on the substrate for
stimulating tissue or sensing electrical activity in the tissue; and

[0124] one or more ribs or spines provided in or on the substrate and
extending some or all of the distance between the proximal and distal
ends of the substrate,

[0125] wherein at least a portion of the substrate is configured for
insertion, via an incision, to a stimulation position between first and
second tissue layers.

[0126] The first and second tissue layers may be layers within the eye,
e.g., the sclera and choroid, or layers other than one or both of the
sclera and choroid, e.g., the layers may be the retina and choroid. The
device may therefore be for episcleral, subretinal or epiretinal use.
Alternatively, the tissue layers may be layers in other parts of the
body, such as tissue layers surrounding the brain, e.g. the dura. The
device may be used in Electroencephalography (EEG) techniques, where
electrical activity within the brain is monitored. The device may be used
in subdural EEG (sdEEG), with the first tissue layer being the dura. The
second tissue layer may be the arachnoid and thus the substrate may
locate in the dura-arachnoid interface region. Alternatively, the
substrate may be arranged to locate in the epidural space adjacent the
spinal cord. Notably, the dura has a similar biological function to the
sclera, discussed with respect to previous aspects. The device can have
applications in cortical EEG, as a seizure monitor and stimulator. The
device may be used in brain and spinal cord stimulation or monitoring,
e.g. to monitor seizure activity and/or to block or prevent seizures and
may utilize temporal lobe electrodes. Spinal cord stimulation may be used
to treat some pain syndromes. The device may be used in cardiology, and
may located under the pericardium for example. Depending on where the
device is used, electrodes may be positioned at different regions of the
substrate, such as a central region of the substrate or even at or
adjacent the proximal end of the substrate.

[0127] The device of any of the eleventh to sixteenth aspects may comprise
any one or more of the features described herein with respect to other
aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0128] By way of example only, embodiments are now described with
reference to the accompanying drawings, in which:

[0129] FIG. 1a shows an oblique side view of a visual prosthesis according
to a first embodiment;

[0130] FIGS. 1b and 1c show cross-sectional views of the prosthesis of
FIG. 1a along lines A-A and B-B of FIG. 1a respectively;

[0131] FIG. 2 shows a cross-sectional side view of the prosthesis of FIG.
1a when located between the sclera and choroid;

[0132] FIG. 3 shows an example electrode and wire topography for the
prosthesis of FIG. 1a;

[0133] FIGS. 4a to 4c represent steps that can be carried out to implant
the prosthesis of FIG. 1a in an eye;

[0134] FIGS. 5a and 5b show side and rear views respectively of an eye
having the prosthesis of FIG. 1a implanted therein;

[0135] FIGS. 6 and 7 show the routing of a cable relative to the skull to
connect the prosthesis of FIG. 1a to a wireless receiver;

[0136] FIG. 8 shows a cross-sectional view of the cable of FIGS. 6 and 7
anchored to a skull;

[0137] FIGS. 9a shows a plan view of a prosthesis according to a second
embodiment, and FIGS. 9b and 9c show cross-sectional views of the
prosthesis along lines A-A and B-B of FIG. 9a respectively;

[0138] FIG. 10a shows a top view of a visual prosthesis according to a
third embodiment, FIGS. 10b and 10c show cross-sectional views of the
perimeter of the prosthesis of FIG. 10a along lines A-A and B-B of FIG.
10a respectively; and FIG. 10d shows a top view of a bottom layer of the
prosthesis of FIG. 10a;

[0139] FIGS. 11 and 12 show top views of bottom layers of visual
prostheses according to two further embodiments, the visual prostheses
being similar to the visual prosthesis of FIG. 10a, but employing helical
wiring;

[0140] FIGS. 13a to 13c represent steps that can be carried out to implant
the prostheses of FIGS. 10 to 12 in an eye; and

[0141] FIGS. 14a and 14b show top and side views, respectively, of a
scleral patch for use with the prostheses of FIGS. 10 to 12.

EMBODIMENTS

[0142] A visual prosthesis 1 according to a first embodiment is shown in
FIG. 1a. The prosthesis 1 comprises an implantable component comprising a
substrate 10 having a distal end 11 and a proximal end 12. The substrate
10, when viewed from above, is substantially rectangular, with curved
corners, its longitudinal direction extending between the distal and
proximal ends 11, 12. Adjacent the distal end 12 of the substrate 10, an
array of electrodes 13 is provided for stimulating retinal cells of an
eye. Each electrode is connected via a separate electrical conductor,
e.g., a biocompatible metal wire 14 such as a platinum wire, to an
electrode interface unit 15. The conductors 14 are electrically insulated
from one another and electrically insulated from surrounding eye tissue
as they extend from the electrode interface unit to the electrodes. The
electrode interface unit is depicted embedded in the substrate 10 at the
proximal end 12. The electrode interface unit 15 is hermetically sealed
to protect electronic components of the electrode interface unit 15 from
damage by body fluids and to protect the patient from exposure to
chemicals contained in the electronic components. An example electrode
and wire topography for the substrate is shown in FIG. 3.
Flexible/photolithographic or lasered wiring and array fabrication can be
employed in the construction of the device. The embodiment of the
electrode interface unit 15 that is depicted comprises a cross-point
switch matrix to enable communication with each electrode individually.

[0143] Referring to FIG. 2, the prosthesis 1 is arranged to be implanted
at least partially between the sclera 21 and the choroid 22 layers of the
eye, via an incision 20 in the sclera 21.

[0144] The implantation steps according to one embodiment of the invention
are represented in FIGS. 4a to 4c. An incision 20 is made in the sclera
with a scalpel 31, the incision 20 being slightly wider than the width of
the substrate 10 (FIG. 4a), and then the distal end 11 of the substrate
10 is pushed into the incision, using soft-tipped forceps 32; through the
scleral layer and into a pocket between the sclera and the choroid (FIG.
4b). Once fully inserted, the opening of the incision is closed using
sutures 33 (FIG. 4c). In this embodiment, the incision 20 is about 5 mm
from the corneal limbus 25.

[0145] Referring again to FIGS. 1a to 1c and FIG. 2, the substrate 10 is
thickest at or near the proximal end 12 and tapers in thickness toward
the distal end 11. (In this embodiment, the substrate 10 tapers from a
maximum thickness of about 1 mm to a minimum thickness of about 0.15 mm).
The resulting wedge shape is well suited to gradually opening up the
pocket (cleavage plane) between the sclera 21 and the choroid 22 as the
distal end 11 is pushed into position, creating space for the thicker
proximal end 12 where the relatively large electrode interface unit 15 is
located. Since the substrate 10 tapers toward the distal end 11, the
distal end is relatively flexible, enabling it to conform to the anatomy
of the sclera and choroid layers as it is pushed into place.
Nevertheless, to prevent buckling as it is pushed forward, a central
spine 16 is provided in a core region of the substrate 10.

[0146] The central spine 16 is an elongate portion embedded in the
substrate between the top surface 101 and bottom surface 102 of the
substrate 10. The spine 16 extends parallel to the longitudinal direction
of the substrate and is located centrally in the lateral direction of the
substrate. The central spine is of stiffer material than the surrounding
substrate and it therefore stiffens the substrate 10, particularly in the
longitudinal direction, but permits enough flexing of the substrate 10,
particularly in the lateral direction (the direction across the width of
the substrate), to allow the substrate to at least substantially if not
wholly conform to the sclera 21 and choroid 22. The controlled
flexibility and stiffness of the substrate 10 enables the substrate 10 to
be pushed into position without introducing a guide into the incision 20.
In alternative embodiments, the wires 14 connecting the electrodes 13 to
the electrode interface unit 15 are bundled together to create one or
more spines, and in other embodiments, ribs on and/or cuts in the
substrate 10 are provided. With reference to FIGS. 1b and 1c, although
the spine 16 is present in both the relatively thick proximal end region
of the substrate 10 (which can have a thickness of about 1 to 1.2 mm for
example) and the relatively thin distal end region of the substrate 10
(which can have a thickness of about 0.3 to 1 mm for example), in
alternative embodiments the spine 16 may be present at the relatively
thin distal end region only, for example. In this regard, the relatively
thick proximal end region of the substrate 10 may have sufficient
stiffness to prevent buckling at that region without the spine 16 being
present. If the substrate 10 comprises silicone, for example, it may
exhibit sufficient stiffness at the proximal region of the substrate 10
without needing a spine 16.

[0147] By having relatively flexible distal end 11, the risk of damage to
the eye tissue, e.g. the optic disc, upon insertion of the substrate 10
may be reduced. Nonetheless, to provide additional protection against
damage, the prosthesis in this embodiment comprises a bumper 17 that
projects from the outer edge of the substrate 10 (see FIG. 3). The bumper
17 is a portion of relatively thin, soft, compliant material, with curved
corners, that can deform when contact with tissue is made. In this
embodiment, the bumper 17 comprises silicone material and extends about 1
to 2 mm from the edge of the substrate.

[0148] The top surface 101 of the substrate 10, which is configured to
face towards the sclera in this embodiment, is curved both longitudinally
and laterally. The degree of curvature in the lateral direction reduces
as the substrate extends toward the distal end 11, as can be seen from a
comparison of FIGS. 1b and 1c.

[0149] When the visual prosthesis 1 is fully implanted, the substrate 10
locates entirely between the sclera 21 and choroid 22. The electrodes 13
locate adjacent the active cells of the eye's retina 23, about 2 mm to
4mm, e.g. 3 mm to one side of the optic disc 24 (see FIGS. 5a and 5b, in
which the location of the substrate under the sclera is indicated by
dotted lines 10'). Meanwhile, a region at the proximal end 12 of the
substrate 10 sits over the incision 20 in the sclera 21.

[0150] The visual prosthesis 1 includes an anchor portion 18, formed of a
relatively thin flap of material, connected to the proximal end 12 of the
substrate. The anchor portion 18 is designed to extend into the incision
20, as shown in FIG. 2, and anchor the proximal end 12 of the substrate
10 thereto. Sutures used to close the incision 20 are also used to
connect the anchor portion 18 to the tissue of the sclera 21.
Accordingly, the proximal end 12 of the substrate 10 is substantially
fixed in position relative to the sclera 21 whilst the distal end 11 of
the substrate `floats` between the sclera 21 and the choroid 22. Once
fixed, part of the anchor portion 18 may be removed, reducing its size,
enabling a greater area of scleral tissue either side of the incision 20
to rejoin. In alternative embodiments, the anchor portion comprises
cut-out central sections to achieve a similar effect.

[0151] A cable 42 extends from the substrate, to connect the electrode
interface to a wireless receiver located externally to the eye, as
discussed further below. The cable 42 extends from the substrate at a
similar position to the anchor portion 18 so that it can exit the eye
through the incision 20. The cable 42 can also provide a form of anchor
portion in addition to the anchor portion 18 discussed above.

[0152] The length of the substrate 10 between its distal and proximal ends
11, 12 is chosen to achieve the desired insertion arrangement. In this
embodiment, the substrate is approximately 15 mm long from its connection
with the anchor portion to the distal tip of the substrate, and the
anchor portion is approximately 3 mm long (at least upon insertion). The
substrate is approximately 8 mm wide.

[0153] The anchor portion 18 is connected to the substrate at a position
about 1 to 3 mm, e.g. 2 mm, inwards from the proximal end edge 121. This
leaves a proximal lip portion 19 of the substrate 10, positioned to the
opposite side of the anchor portion 18 to the distal end 11 of the
substrate 10. As can be seen in FIG. 2, the lip portion 19 ensures that
the substrate 10 abuts the surface of the sclera 21 either side of the
incision 20, ensuring that the anchor portion 18 is positioned in a
balanced manner in the incision 20, and generally enhancing the stability
of the device 1 and sealing of the incision at this region.

[0154] The visual prosthesis 1 forms part of a vision restoration
apparatus. The apparatus includes an image receiver (e.g. a video camera)
for receiving a stream of images, which may be positioned on eye glass
frames; an image processor for converting the stream of images received
by the image receiver into electrical signals, which may also be
positioned on the eye glass frames; a wireless transmitter connected to
the image processor for transmitting the electrical signals wirelessly,
which may also be positioned on the eye glass frames; and a wireless
receiver connected to the electrode interface unit for receiving the
electrical signals from the wireless transmitter.

[0155] With reference to FIGS. 6 and 7, in the present embodiment, the
wireless receiver 41 is implanted at the rear of the patient's head. The
cable 42, which may be a helical cable with high flexibility, is
connected between the wireless receiver 41 and the electrode interface
unit 15. By having high flexibility, the cable 42 may be implanted
relatively easily, and the cable 42 may flex as the eye 2 is rotated,
without causing damaging to tissue as it exits the incision 20 in the
sclera 21.

[0156] The cable 42 extends from the electrode interface unit 15, through
the incision 20 in the sclera 21 and along the side of the user's skull
43 to the wireless receiver 41. To hold the cable 42 in position as it
extends out of the incision 20 and along the side of the user's skull 43,
a plurality of anchors 44, 45 are provided. The anchors 44 each comprise
an open Dacron® mesh and extend over, and are adhered to, the cable
42, as shown in FIG. 8. Opposite sides of the anchors 44, 45 are fixed to
the sclera/side of the user's head using sutures 46, e.g., Nylon 8.0
sutures. The anchors 44, 45 are Parylene coated with silicone to reduce
adhesion between the anchors 44, 45 and body tissue. One of the anchors
45 is located adjacent the incision 20 in the sclera 21, ensuring that
the cable 42 exits the incision 20 in a secure manner, preventing damage
to the sclera 21 as the cable 42 flexes, e.g. due to rotation of the eye
2. The incision 20 and anchor 45 are strategically positioned on the
sclera 21 to avoid interfering with the extraocular muscles. In this
embodiment, the incision 20 is positioned in front of the connection
between the eye and the lateral rectus muscle, and the anchor is
configured to direct the cable rearward, over the top of the lateral
rectus muscle and between the lateral rectus muscle and the superior
rectus muscle.

[0157] In this embodiment, the cable 42 is provided with at least two
different diameters as it extends between the electrode interface unit 15
and the wireless receiver 41. In particular, the cable 42 has a
relatively small first diameter as it extends through the incision 20 in
the sclera 21 allowing maximum closure of the incision after implantation
to be achieved, and a relatively large second diameter as it extends
onwards to the wireless receiver 41 providing the cable 42 with increased
strength at this region. For example, the cable 42 may have the second
diameter where it extends from the eye socket 47 around a relatively
sharp turn to the temple region 48 of the skull 43. In this embodiment,
the first diameter is between 0.2 and 1 mm, e.g., 0.64 mm, and the second
diameter is between 1 mm and 2 mm, e.g., 1.19 mm. The cable 42 has the
first diameter for about 30 mm of its length from its connection point
with the electrode interface unit/substrate, and the second diameter for
at least the next 30 mm of its length.

[0158] In alternative embodiments, the wireless receiver may be located on
the surface of the eye (episclerally), rather than to the rear of the
head.

[0159] A visual prosthesis 100 according to a second embodiment is shown
in FIGS. 9a to 9c. The prosthesis 100 has substantially the same
configuration and functionality as the prosthesis 1 according to the
first embodiment, including a substrate 110 extending between distal and
proximal ends 111, 112, an electrode array 113 and a bumper 117. However,
the proximal end 112 of the substrate in this embodiment is wider than
the distal end 111. In this regard, the substrate 110 has a "T" shape
when viewed from above (see FIG. 9a). This enables a larger electrode
interface unit 115 to be used. In this embodiment, the electrode
interface unit 115 actually comprises two cross point switch matrices
1151 that are spaced apart. By spacing the matrices apart, a central
region 1152 between the two matrices 1151 can provide a bending point in
the lateral direction of the substrate 110 (see FIG. 9b in particular),
enabling the substrate to conform more closely to the anatomy of the
sclera and choroid. Another difference over the first embodiment is the
provision of the anchor portion 118 at the proximal end edge of the
substrate 110.

[0160] A visual prosthesis 200 according to a third embodiment is shown in
FIGS. 10a to 10d. Like the prosthesis 1 of the first embodiment, the
prosthesis 200 includes an elongate substrate 210 extending between
distal and proximal ends 211, 212, an electrode array 213, and a cable
242 connected to the electrode array 213.

[0161] In this embodiment, the prosthesis 200 does not comprise a
dedicated anchor portion connected to the substrate. Rather, the
prosthesis relies at least in part in the cable 242 extending through the
scleral incision to provide an anchor portion, assisting in anchoring of
the prosthesis 200 after insertion into the eye. A lip portion 219
(stabilising tail) of the substrate is provided to the proximal side of
the connection point of the cable 242 and the substrate 210. The
stabilising tail 219 ensures that the substrate abuts the surface of the
sclera 21 either side of the incision 20 in which the cable 242 locates,
enhancing the stability of the device at that region and improving
sealing. The stabilizing tail 219 may be tucked into position after the
distal end of the substrate has reached its stimulation position.

[0162] Prior to implantation, with reference to FIGS. 10b and 10c, the
bottom surface 202 of the substrate 210, which is configured to face
towards the choroid, is substantially flat and the top surface 201 of the
substrate 210, which configured to face towards the sclera, is curved in
both the longitudinal and lateral directions of the substrate 210. The
substrate 210 is thickest at an intermediate region 203 between the
distal and proximal ends 211, 212, the intermediate region 203 being
closer to the proximal end 212 than the distal end 211. Accordingly, the
substrate tapers in the longitudinal direction from the intermediate
region 202 towards both the proximal end 212 and the distal end 211, but
the length of the distal taper is greater than the proximal taper.
Therefore, the substrate 210 is most flexible toward its distal end 212.

[0163] Referring to FIG. 10c, in the lateral direction, the top surface
201 has a part spherical profile that continues until it meets the bottom
surface 202 at the lateral sides 204 of the substrate 210. Accordingly,
in the lateral direction, the substrate 210 is more flexible towards the
lateral sides 204.

[0164] The curved profile of the top surface 201, and the flexibility of
the substrate 210, allows the substrate to conform substantially to the
curved shapes of the choroid and scleral layers of the eye. Although the
bottom surface 202 is flat prior to implantation, upon implantation, the
substrate 210 can flex and the bottom surface 202 can take a curved
configuration.

[0165] In this embodiment, the substrate is formed from four separately
moulded layers 210a-210d that are bonded together to form a substrate 210
of laminar construction. The electrode array 213 is located on the bottom
layer 210a. The layers 210a-210d have substantially the same thickness,
but the dimensions of each layer in the lateral and longitudinal
directions of the substrate become progressively smaller from the bottom
layer 210a to the top layer 210d. Once the layers 210a-210d are bonded
together, the edges of the layers 210a-210d may be rounded off to achieve
a smooth, curved top surface 201. In alternative embodiments, the
substrate may be formed from a single moulded element only, or via other
methods.

[0166] With reference to FIG. 10d, which shows the bottom layer 210a only,
it can be seen that an electrode interface unit is not provided in the
substrate of the present embodiment. Instead, the electrode array 203,
and two return electrodes 205, are each connected to electrical
conductors 206, e.g., wires, which bundle together in the cable 242 and
extend from the substrate to an electrode interface unit located remotely
from the substrate 210 (not shown). The return electrodes 205 project
from the bottom layer 210a of the substrate 210, and therefore an opening
may be provided in at least the adjacent layer 210b of the substrate to
accommodate the return electrodes 205.

[0167] With reference to FIG. 10a, when viewed from above, the substrate
210 is substantially rectangular, with curved corners, and the cable 242
extends from one side 204 of the substrate 210 adjacent the proximal end
211, in a direction substantially perpendicular to the longitudinal
direction of the substrate. Accordingly, the substrate is configured for
implantation to the lateral side of one eye (the right eye). Although not
shown, a corresponding prosthesis for implantation via an incision on the
lateral side of the opposite eye (the left eye) would have a cable
extending substantially from the opposite side 204 of the substrate
adjacent the proximal end 211.

[0168] With reference to FIGS. 12 and 13, in certain embodiments, helical
wiring may be employed to communicate electrically with the electrodes
213 in place of the flexible/lasered circuit lead shown in FIG. 10d, for
example. The helical wiring can form part of a helical cable 243
extending from the substrate, as shown in FIG. 12, or it may also be
helical in form as it extends internally within the substrate, as shown
in FIG. 13. Coiling the wire and cable allows for stretching as the
substrate flexes or the cable flexes, e.g., during insertion of the
substrate in the eye or during subsequent use of the implanted substrate,
e.g. when the eye rotates. The helical wire can be helical 25 μm
platinum wire, for example.

[0169] Implantation steps according to an embodiment of the invention,
suitable for implanting the devices of FIGS. 10 to 12 in an eye, are
represented in FIGS. 13a to 13d. An L-shaped incision 220 is made in the
sclera with a scalpel 231, the L-shaped incision comprising a
substantially vertical cut 221, and a substantially horizontal cut 222,
in the surface of the sclera, the horizontal cut 222 extending rearward
from the top of the vertical cut 221 (FIG. 13a). The vertical cut is
slightly wider than the width of the substrate 210 and extends the full
depth of the sclera at that point. After making the incision, a pocket is
created between the sclera and the choroid using the scalpel 231 or
further curved or crescent-shaped blade (FIG. 13b). The blade is extended
through the incision and is manipulated in order to cleave the sclera and
choroid apart. The pocket thus created extends from the end of the
incision partway toward the stimulation position under the area centralis
or macula. Using soft-tipped forceps 232, the distal end 211 of the
substrate 210 is pushed through the vertical cut 221 and through the
scleral layer into the pocket between the sclera and the choroid (FIG.
13c). A marker 2101 is provided on the top surface 201 of the substrate
210 to indicate when the substrate will have reached the end of the
pocket. The pocket ensures that the substrate 210 is positioned in the
appropriate anatomical plane between the sclera and choroid prior to
further advancing of the distal end 211 of the substrate to the final
stimulation position. After the distal end 211 reaches the stimulation
position, the stabilizing tail 219 of the substrate is tucked into
position between the sclera and choroid, to the opposite side of the
incision to the distal end 211 of the substrate, ensuring that the entire
substrate locates between the sclera and choroid and the substrate fits
over the incision in a stable, sealed, manner.

[0170] Due to the flexible, robust, construction of the substrate 210, the
substrate can tunnel forward relatively easily through tissue and can be
manipulated (e.g., turned) accurately to arrive at the stimulation
position, while contact with the optic disc is avoided. During insertion,
and once fully inserted, since the cable 242 extends from the substrate
210 substantially perpendicular to the longitudinal direction of the
substrate, the cable 242 connected to the substrate 210 can extend
through the horizontal cut 222, ensuring that the cable 242 does not
obstruct insertion of the substrate 210 along a desired insertion path.
After insertion, an anchor 245 connected to the cable 242 is fixed to the
side of the eye 2 using sutures 233 to maintain the cable 242 in
position. The opening of the incision 220 is then closed using sutures
233 (FIG. 13d). In this embodiment, the vertical cut of the incision 220
is about 5 mm from the corneal limbus 25.

[0171] The anchor 245 is shown in more detail in FIGS. 14a and 14b. The
anchor 245 takes the form of a substantially square patch 245. The patch
245 extends over the cable 242 at the incision 220 and is sutured to the
sclera 2 to fix the cable 242 to the sclera 2. The path of the cable 242
underneath the patch is shown by dotted lines in FIG. 15a. As can be
seen, as the cable 242 exits the incision 220, it extends in a
substantially vertical direction. However, the patch 245 is configured to
fix an approximately 90 degree bend in the cable 242 so that the cable
extends from underneath the patch 245 in a substantially horizontal
direction, towards the rear of the patient's skull. In this embodiment,
the underside of the patch 245 is adhered to the cable 242 using glue 246
at one side of the patch only.

[0172] It will be appreciated by persons skilled in the art that numerous
variations and/or modifications may be made to the invention as shown in
the specific embodiments without departing from the scope of the
invention as broadly described. The present embodiments are, therefore,
to be considered in all respects as illustrative and not restrictive.